High Volumetric Energy Density Asymmetric Fibrous Supercapacitors with Coaxial Structure Based on Graphene/MnO 2 Hybrid Fibers

One-Step Wet-Spinning of High-Energy Density Coaxial Fibrous Supercapacitors Based on In Situ Carbon-Modified Nitrogen-Doped MXene Nanosheets

Fibrous supercapacitors (SCs) are emerging promising power sources for flexible/wearable electronics and have attracted an extensive amount of attention from researchers. However, the low energy density has always hindered their further development. Here, a coaxial fibrous SC (CFSC) was fabricated by one-step wet-spinning combined with an electrodeposition strategy. Benefiting from the large surface area and abundant pore structure of carbon-modified nitrogen-doped MXene nanosheets (NS), as well as the high conductivity of silver (Ag) NS, the electrolyte ion/electron transport paths are significantly improved. Furthermore, the distributed GO in the P(VDF-HFP) separator could form a high-speed continuous ion transport channel, thus enhancing the ionic conductivity. At a power density of 40-200 μW cm-2, the CFSC shows a high energy density of 0.7-3.39 μWh cm-2. The as-prepared CFSC also maintains an excellent capacitance retention rate of 90.3% even after 15 000 charge-discharge cycles. This work provides a general strategy for manufacturing high-performance, flexible, and wearable SCs.

Graphene-based implantable neural electrodes for insect flight control

Implantable neural electrodes have been widely used to investigate the function of the brain and treat neurological disorders. Due to their advantages of size and preparation, fibrous neural electrodes have been widely applied, but conventional metal wire electrodes have many shortcomings that are impossible to overcome. Here, we present a modified graphene-based fiber electrode, which retains the excellent electrical properties of the graphene fiber (GF) electrode and enhances the charge storage capacity (CSC) from the initial 7.97 mC cm^-2 to 504.04 mC cm^-2. The modified electrodes were further investigated via in vivo experiments, and the results show that the modified graphene fibers controlled insect flight with a minimum voltage close to that of silver wire electrodes, and no irreversible chemical reaction occurred during the electrical stimulation process, which could achieve the stimulation effect while ensuring the safety of the tissues around the electrodes.

Recent Progress in Flexible Graphene-Based Composite Fiber Electrodes for Supercapacitors

Graphene has shown the world its fascinating properties, including high specific surface area, high conductivity, and extraordinary mechanical properties, which enable graphene to be a competent candidate for electrode materials. However, some challenges remain in the real applications of graphene-based electrodes, such as continuous preparation of graphene fibers with highly ordered graphene sheets as well as strong interlayer interactions. The combination of graphene with other materials or functional guests hence appears as a more promising pathway via post-treatment and in situ hybridism to produce composite fibers. This article firstly provides a full account of the classification of graphene-based composite fiber electrodes, including carbon allotropy, conductive polymer, metal oxide and other two-dimensional (2D) materials. The preparation methods of graphene-based composite fibers are then discussed in detail. The context further demonstrates the performance optimization of graphene-based composite fiber electrodes, involving microstructure design and surface modification, followed by the elaboration of the application of graphene-based composite fiber electrodes in supercapacitors. Finally, we present the remaining challenges that exist to date in order to provide meaningful guidelines in the development process and prospects of graphene-based composite fiber electrodes.

High-Performance Coaxial Asymmetry Fibrous Supercapacitors with a Poly(vinyl alcohol)-Montmorillonite Separator

Fibrous supercapacitors have garnered great interest from researchers because of their large electrode/electrolyte interface area, short ion transport path, and high flexibility. However, obtaining a thin gel electrolyte interlayer with a high ion transport rate and uniform thickness is still challenging. Here, we proposed an efficient wet-spinning technique to fabricate uniform polyvinyl-montmorillonite tubular layers for the preparation of a high-performance coaxial asymmetry fibrous supercapacitor (AFSC). The coaxial AFSC shows ultrahigh energy densities in the range of 2.86-4.04 μW h cm^-2 at power densities of 0.16-1.61 mW cm^-2 while maintaining a long cycling life (94% retention even after 20 000 cycles). After charging at a constant voltage of 2.4 V for 30 s, the flexible watchband which is composed of three series-connected AFSCs could power a commercial electronic watch for more than 2 min. This work provides a universal strategy to fabricate high-performance and wearable energy storage devices.